The present invention relates to a method and an apparatus for treating an exhaust gas containing a fluorine-containing compound. More particularly, the invention relates to a treatment method and a treatment apparatus for efficiently decomposing C2F6, C3F8, CF4, CHF3, SF6 or NF3 which is discharged in the step of dry cleaning the internal surface, etc. of a chamber or the like of semiconductor manufacturing equipment with the use of C2F6, C3F8, CF4, CHF3, SF6 or NF3 in the semiconductor industry, or during etching of various films on a semiconductor device.
In the semiconductor industry, many kinds of hazardous gases are used in the semiconductor manufacturing process, arousing concern for environmental contamination by them. C2F6, contained in an exhaust gas from a chemical vapor deposition (CVD) step and an etching step, acts as a global warming gas, and the establishment of a system for its removal is considered to be an urgent task.
In dry etching a silicon wafer or the like with the use of a manufacturing apparatus for a semiconductor device, such as an etching apparatus, for example, fluorinated hydrocarbons, such as CF4, CHF3, and C2F6, are used. In an exhaust gas from the etching apparatus, fluorinated hydrocarbons, such as CF4, CHF3, and C2F6, are contained.
An exhaust gas containing a fluorine-containing compound may be discharged during cleaning of a manufacturing apparatus for a semiconductor device. To form a thin film on a semiconductor substrate, a chemical vapor deposition apparatus is used as a semiconductor device manufacturing apparatus. When thin films adhering to a chamber and an internal surface of piping in the chemical vapor deposition apparatus are cleaned with a ClF3 gas, an exhaust gas including various fluorine-containing gases is discharged from the chemical vapor deposition apparatus.
Various decomposition techniques and recovery techniques have been proposed as methods for treating fluorine-containing compounds such as C2F6. As the decomposition technology, in particular, the use of compounds, such as Pt catalysts, zeolite-based catalysts, activated carbon, active alumina, alkali metals, alkaline earth metals, and metal oxides, is named as a method of catalytic thermal decomposition. However, none of methods using them have been found effective.
Of the conventional technologies, the method of catalytic thermal decomposition comprises decomposing C2F6 by passing it through a heated catalyst. However, all of the methods of this type have involved drawbacks, such as a low decomposition rate, a short life of the treating agent, and occurrence of carbon monoxide (CO) as a by-product which is difficult to treat.
Under these circumstances, the present invention aims to solve the above-described problems with the earlier technologies, and provide a method and an apparatus for treating an exhaust gas containing a fluorine-containing compound, the method and apparatus having a high decomposition rate, being effective for long periods, and involving minimal occurrence of carbon monoxide (CO).
According to an aspect of the present invention, there is provided a method for decomposing a fluorine-containing compound in an exhaust gas by contacting the exhaust gas containing the fluorine-containing compound with aluminum oxide at a high temperature enough to decompose the fluorine-containing compound.
In the present invention, the above contacting step is preferably performed in the presence of a hydrogen gas (H2) in a molar amount in excess of the amount required to convert the fluorine atoms in the fluorine-containing compound to HF. More preferably, the contacting step is performed in the presence of 1.5 or more times as many as the molar amount of a hydrogen gas (H2) required to convert the fluorine atoms in the fluorine-containing compound to HF.
Preferably, the contacting step is performed in the presence of an oxygen gas whose amount is not less than the number of moles of the hydrogen gas.
Preferably, the fluorine-containing compound contains a carbon atom, a sulfur atom, or a nitrogen atom, and the contacting step is performed in the presence of an oxygen gas (O2) in a molar amount in excess of the amount required to convert the carbon atom to CO2, the sulfur atom to SO2, or the nitrogen atom to NO2.
The aluminum oxide preferably includes xcex3-alumina. Preferably, the aluminum oxide is particulate.
The high temperature is preferably in the temperature range of about 800xc2x0 C. to about 900xc2x0 C.
The fluorine-containing compound preferably includes C2F6, C3F8, CF4, CHF3SF6 or NF3. The exhaust gas preferably has been discharged from a semiconductor device manufacturing apparatus.
It is preferred to remove a catalytic poison to the aluminum oxide from the exhaust gas, and then perform the contacting step. It is further preferred to remove SiF4 from the exhaust gas, and then perform the contacting step.
Preferably, the step of removing an acidic gas is present after the contacting step. Further preferably, the acidic gas is removed using water.
According to another aspect of the present invention, there is provided an apparatus for treating an exhaust gas containing a fluorine-containing compound, which includes a vessel for accommodating aluminum oxide, and a passage for passing the exhaust gas containing the fluorine-containing compound into the vessel.
In the present invention, it is preferred to further include a heater capable of heating the aluminum oxide to a high temperature enough to decompose the fluorine-containing compound.
It is preferred to further include a feeder for feeding a hydrogen gas (H2) in a molar amount in excess of the amount required to convert the fluorine atoms in the fluorine-containing compound to HF.
Preferably, a feeder for feeding an oxidizing agent is further included.
Preferably, the fluorine-containing compound contains a carbon atom, a sulfur atom, or a nitrogen atom, and there is further included a feeder for feeding O2 in a molar amount in excess of the amount required to convert the carbon atom to CO2, the sulfur atom to SO2, or the nitrogen atom to NO2.
The aluminum oxide preferably includes xcex3-alumina. More preferably, the aluminum oxide is particulate.
The passage is preferably connected to an outlet of a semiconductor device manufacturing apparatus.
The vessel is preferably a packed column.
Preferably, a pretreatment apparatus for removing a catalytic poison to the aluminum oxide from the exhaust gas is further present upstream from the vessel. Also preferably, a pretreatment apparatus for removing SiF4 from the exhaust gas is further present upstream from the vessel.
Preferably, a posttreatment apparatus for removing an acidic gas is further placed downstream from the vessel. The posttreatment apparatus preferably removes the acidic gas by use of water.
According to still another aspect of the present invention, there is provided a method for producing a semiconductor device, including the steps of:
etching a precursor of the semiconductor device with an etching gas containing a fluorine-containing compound or a plasma thereof in a chamber;
discharging an exhaust gas containing a fluorine-containing compound from the chamber; and
contacting the exhaust gas with aluminum oxide at a high temperature enough to decompose the fluorine-containing compound, thereby decomposing the fluorine-containing compound in the exhaust gas.
Preferably, the contacting step is performed in the presence of a hydrogen gas (H2) in a molar amount in excess of the amount required to convert the fluorine atoms in the fluorine-containing compound to HF.
According to a further aspect of the present invention, there is provided a method for producing a semiconductor device, including the steps of:
forming a thin film in a chamber of a chemical vapor deposition apparatus by chemical vapor deposition of a thin film-forming gas on a precursor of the semiconductor device;
withdrawing the resulting semiconductor device from the chamber;
cleaning the chamber of the chemical vapor deposition apparatus with a cleaning gas containing a fluorine-containing compound; and
contacting an exhaust gas containing a fluorine-containing compound from the cleaning step with aluminum oxide at a high temperature enough to decompose the fluorine-containing compound, thereby decomposing the fluorine-containing compound in the exhaust gas.
Preferably, the contacting step is performed in the presence of a hydrogen gas (H2) in a molar amount in excess of the amount required to convert the fluorine atoms in the fluorine-containing compound to HF.